King County prosecutors contend Timothy Funkhouser admitted to taking the videos while working out of the Sea-Tac Airport light rail station.
Funkhouser, 35, was reported in March after showing another Securitas security guard a video he'd taken of a customer, a King County detective told the court.
According to charging papers, Funkhouser showed his coworker a six-minute video consisting only of "a continuous crotch shot" of a young woman or girl seated on a Sound Transit train. Funkhouser is alleged to have told his coworker he took the video surreptitiously with his iPhone.
Later that day, the other guard watched as Funkhouser followed a young woman onto an escalator. The guard told police Funkhouser placed his cell phone on the escalator step underneath the woman to film up her skirt.
Funkhouser was suspended the following day.
Writing the court, the detective noted Funkhouser told a Securitas human resources worker he took the videos but planned to lie about it, and that he would never trust his coworkers again. Funkhouser is alleged to have then explained to the human resources worker how he took the offending photos.
Police subsequently searched Funkhouser's Federal Way home, where they seized computers, cell phones and cameras. Investigators found several voyeuristic photos on Funkhouser's home computer and cell phone; it wasn't immediately clear to police whether Funkhouser took those videos himself or found them online.
Funkhouser is alleged to have admitted taking videos on two or three other occasions. Asked why he tried to record the woman on the escalator, Funkhouser allegedly explained he "had to try."
Charged with one count of voyeurism, Funkhouser has not been jailed. He has no criminal history.
Funkhouser worked as a driver for the car-sharing service Lyft earlier this year.
The search warrant that led to the voyeurism charge was served in March, but Lyft said Funkhouser began working with them in May. The company said it does extensive background checks.
Funkhouser came back clean when he was hired and had no criminal history. Lyft terminated him when they learned he had been charged.